Generally, mobile communication systems have been developed, aiming to provide communication while securing mobility of users. Due to the rapid development of technologies, the mobile communication systems now can provide not only voice communication services but also high-speed data communication services. Recently, standardization for Long Term Evolution (LTE), one of the next-generation mobile communication systems, is in progress in 3rd Generation Partnership Project (3GPP). LTE is a technology aimed to be commercialized in around 2010 and implementing high-speed packet-based communications at a data rate as high as 100 Mbps, which is higher than that currently available. Recently, many discussions have been made to provide various new services to LTE communication systems. A typical one of the technologies to be newly introduced may include Machine To Machine, Machine Type Communication (hereinafter referred to as ‘M2M/MTC’) communication.
M2M/MTC communication, also known as inter-device communication, refers to communication between an electronic device and an electronic device, or between an electronic device and a data server over a mobile communication network. In early 1990s when the concept of the M2M/MTC communication was first introduced, the M2M/MTC communication was considered the concept of remote control, telematics, or the like and its derivatives market was very limited, but the M2M/MTC communication has grown into a big worldwide market for the last few years with the fast growth. The M2M/MTC technology may be used in the field of automotive telematics, logistic management, intelligent metering system, remote asset management system, Point-Of-Sale (POS) system, and security-related industry. Compared with the existing mobile phones used in the mobile communication system, M2M/MTC devices are recommended to operate in an HPSRM mode with a low-power transmission power unit in order to reduce the price of M2M/MTC communication modules. Otherwise, the price of the M2M/MTC devices may increase, hindering the widespread use of the M2M/MTC devices.
FIG. 1 illustrates a configuration example of a 3GPP UMTS/GPRS mobile communication system.
Referring to FIG. 1, a User Equipment (UE) 101 means a terminal device or a subscriber participating in the wireless communication, and the UE 101 is wirelessly connected to a Node B (NB) 105. Node Bs 105, 110, 115, 120, 125, and 130, wireless base station devices directly participating in communication with UEs, manage their own cells. Radio Network Controllers (RNCs) 140 and 145 control a plurality of Node Bs, and control radio resources. The RNCs 140 and 145 are connected to a Packet Switched or Packet Service (PS) network by a Serving GPRS Support Node (SGSN) 150. Connections between the RNCs 140 and 145 and the SGSN 150 are called an IuPS interface, and transmit/receive PS control signaling. The SGSN 150 takes charge of various control functions, and manages mobility of idle mode UEs. The SGSN 150 manages service billing-related data of each subscriber, and controls a function of selectively transmitting and receiving the data it should exchange with the UE 101, by means of the Serving RNC (SRNC) 140 managing the UE 101. A Serving Gateway (S-GW) 160, a device providing data bearers, generates/removes data bearers under control of the SGSN 150.
FIG. 2 illustrates a configuration example of a 3GPP LTE mobile communication system.
Referring to FIG. 2, a Radio Access Network (RAN) of the LTE mobile communication system includes evolved Node Bs (eNBs) 205, 210, 215, and 220, a Mobility Management Entity (MME) 225, and a Serving Gateway (S-GW) 230. A UE 235 accesses an external network via the ENB 205 and the S-GW 230. Each of the ENBs 205 to 220 corresponds to a combined entity of the legacy NB and its RNC in the UMTS system described with reference to FIG. 1.
The ENB 205 is connected to the UE 235 through a wireless channel, and performs a more complex function than the legacy NB. In LTE, since all user traffics including real-time services based on the Internet Protocol (IP), such as Voice over IP (VoIP), are serviced through a shared channel, devices for performing scheduling by collecting status information of UEs are required, and this operation is controlled by the ENBs 205 to 220. The ENBs 205 to 220 take charge of controlling radio resources of their cells. One ENB generally controls a plurality of cells.
To achieve the data rate as high as 100 Mbps, LTE uses Orthogonal Frequency Division Multiplexing (OFDM) as a wireless access technology in a bandwidth of a maximum of 20 MHz. In addition, LTE employs Adaptive Modulation & Coding (AMC) that adaptively determines a modulation scheme and a channel coding rate depending on the channel status of UEs. The S-GW 230, a device providing data bearers, generates/removes data bearers under control of the MME 225. The MME 225, a device for taking charge of various control functions and performing mobility management for idle mode UEs, is connected to a plurality of ENBs.
FIG. 3 illustrates an example of an existing paging procedure in a 3GPP LTE/UMTS/GPRS system, in which for convenience of description, the conventional paging procedures both in the LTE system and the UMTS/GPRS system are illustrated together.
In FIG. 3, reference numeral 301 represents a UE (or M2M/MTC device), reference numerals 302 and 304 represent an eNB and an MME, respectively, and reference numerals 303 and 305 represent an RNC/BSC and an SGSN, respectively, constituting the UMTS/GPRS system. The Base Station Controller (BSC), an entity for controlling radio resources in the GPRS system, performs a similar function to that of the RNC in the UMTS system. Reference numeral 306 represents an S-GW in the LTE/UMTS/GPRS system. Reference numeral 31 represents a paging reception time applied to the existing UE in the LTE system, and the paging reception time refers to a specific radio frame, or a subframe in the radio frame. Reference numeral 32 represents a paging reception time applied to the existing UE in the UMTS/GPRS system, reference numeral 33 represents a paging Discontinuous Reception (DRX) cycle in the LTE system, and reference numeral 34 represents a paging DRX cycle in the UMTS/GPRS system.
Referring to FIG. 3, upon receiving DownLink (DL) data for a specific UE, the S-GW 306 transmits a DL Data Notification message indicating the reception of the DL data for a UE, to the MME 304 and the SGSN 305, which are controlling the UE 301, in steps 331a and 331b. Upon successfully receiving the DL Data Notification message, the MME 304 and the SGSN 305 transmit to the S-GW 306 a DL Data Notification ACK message indicating their successful reception of the DL Data Notification message in steps 313a and 313b. 
The MME 304 and the SGSN 305 transmit a Paging message to the eNBs 302 and the RNCs/BSCs 303 existing in a paging area (e.g., Routing Area (RA) of the UMTS system and Tracking Area (TA) of the LTE system) where the UE 301 is located, in steps 321a and 321b, respectively. The Paging message includes Identification (ID) information of the UE 301 subjected to paging, and information based on which the eNB 302 and the RNC/BSC 303 can calculate when they should transmit the Paging message on a wireless/radio basis. For example, the latter information includes a UE paging DRX cycle and a UE identity index value or UE id, which are used as input values for calculating a radio frame and a subframe carrying the Paging message. For more details, reference can be made to 3GPP standard TS36.413.
Upon receiving the Paging messages in step 321a and 321b, the eNB 302 and the RNC/BSC 303 calculate a time/timing for which they will wirelessly transmit a Paging message for a target UE, based on information included in the received Paging messages. This is because an idle mode UE, performing a power saving operation, generally wakes up at intervals of a paging DRX cycle and checks whether a Paging message is received at the wake-up timing, in step 331.
That is, the eNB 302 and the RNC/BSC 303 should transmit a Paging message for the UE 301 in sync with the timing (e.g., a specific subframe in a specific radio frame in the LTE system) for which the UE 301 wakes up to receive a Paging message at intervals of the paging DRX cycle. Otherwise, the UE 301 may fail to receive the Paging message. Therefore, in terms of the input values, the method in which the UE 301 calculates in step 331 a timing for which it wakes up to receive its Paging message, should be the same as the method in which having received the Paging message in steps 321a and 321b, the eNB 302 and the RNC/BSC 303 calculate a timing for which they will transmit Paging messages for the UE 301. The UE 301 uses its UE id and a paging DRX cycle to calculate a timing for which it will receive a Paging message, while the eNB 302 and the RNC/BSC 303 use the UE id or UE id index, and the paging DRX cycle to calculate a timing for which they will transmit their Paging messages to the UE 301. For more details, reference can be made to the 3GPP UMTS standards TS25.304 and TS25.413, and the 3GPP LTE standards TS36.304 and TS36.413.
Referring to FIG. 3, the eNB 301 and the RNC/BSC 302 transmit Paging messages at intervals of the paging DRX cycle in sync with the paging reception timing of the UE 301 (in steps 351a & 353a in the LTE system, or in steps 351b & 353b in the UMTS/GPRS system). If the UE 301 has failed to receive the transmitted Paging message due to a wireless error in steps 351a and 351b, the UE 301 does not access the system since it has no knowledge of the transmission of the Paging message. In this case, since there is reply to the Paging message, the eNB 302 and the RNC/BSC 303 retransmit the Paging message in steps 353a and 353b, considering that the UE 301 has failed to receive the Paging message. Upon successfully receiving the Paging message retransmitted in steps 353a and 353b, the UE 301 will make access to the system in step 361, and upon detecting the access, the eNB 302 and the RNC/BSC 303 stop the transmission of the Paging message, determining that the UE 301 has successfully received the Paging message. In the absence of the access by the UE 301, the eNB 301 and the RNC/BSC 303 may retransmit the Paging message N1 times (the predetermined number of retransmissions) or for a time of a T1 timer.
However, the above-described procedure of FIG. 3 merely shows an operation of receiving a Paging message by a UE such as the existing mobile phone in an idle mode. If an M2M/MTC device (or UE) supporting the HPSRM mode (hereinafter referred to as an ‘HPSRM M2M/MTC device’) performs the procedure of FIG. 3 in an idle mode, the effects of the HPSRM mode may not be expected. Therefore, there is a need to newly define a paging procedure for M2M/MTC devices operating in the HPSRM mode using a low-power transmission power unit in the mobile communication network.